Poll numbers in Mexico don't seem to support Andres Manuel Lopez Obrador's optimism, but his die-hard supporters see him as the only hope for real change.

TLAXCALA, Mexico — His razor-thin defeat in the 2006 presidential election spiraled into a contentious political melodrama that divided Mexican society after he refused to accept the results.

Now Andres Manuel Lopez Obrador is running again, his second and presumably last attempt to become Mexico's first leftist president in modern times.

"We are going to win the presidency of the country once more," the former mayor of Mexico City proclaimed triumphantly during a campaign stop last week in this small colonial center east of the capital.

Once again, his optimism may belie the facts on the ground. In national polls, he continues to lag far behind Institutional Revolutionary Party candidate Enrique Peña Nieto, although he says his own internal polling shows him running neck and neck.

Lopez Obrador, of the Democratic Revolution Party, or PRD, has been gaining slightly in national polls since the race began in March, capitalizing on discontent with two successive governments under the ruling National Action Party, or PAN, and on lingering distrust of Peña Nieto and the Institutional Revolutionary Party, or PRI.

Wrapped in a long wool serape thrown on him as he inched his way through throngs of supporters, Lopez Obrador described his "adversaries" as "desperate," detailing what he views as a conspiracy of television and political propaganda to "impose" front-runner Peña Nieto on the public.

The crowd booed, jeered and banged on drums. "May God never will it," a woman huffed near the podium.

This week, Lopez Obrador called on PRD supporters to be vigilant observers at polling places Sunday in case the PRI or PAN attempted to steal votes or stuff ballot boxes, which his campaign claims occurred widely in 2006.

Silver-haired at 58, Lopez Obrador inspires fervent passion in supporters — and profound angst among his many critics.

In the 2006 campaign, future president Felipe Calderon called him a "danger to Mexico," and rivals paint him as a potential Mexican Hugo Chavez, the polarizing leftist president of Venezuela.

Lopez Obrador calls it part of a "dirty war" being waged against him.

That rings true with supporters, many of whom see him as the only option for "real change" in Mexico, a sort of heir of the great liberal leaders of Mexico's past.

"I voted for him in 2006. I am a die-hard. I'm not bought off," said Juan Marquez Aguila, 32, a vendor in Tlaxcala who recently returned from the United States. "He does have good ideas. It's not fair that a few are still rich and the people remain poor."

But despite efforts to present himself as a more moderate candidate in search of a "loving republic," he can often dip into the sort of vitriolic discourse that turned off many voters in 2006. Here in Tlaxcala, he called PRI and PAN politicians "pigs" and "hogs" who abuse public funds. The crowds cheered him on.

He hemmed and hawed when asked in a television interview if he would respect the final results.

Yet beneath the sometimes fiery words, his economic and security plans are at their core mainstream and similar to those of his rivals, analysts say. He's reached out to the financial sector and Mexico's business communities, and met with Vice President Joe Biden when he was in the country. Observers say he's even managed to gain support among dissidents in the powerful network of entrepreneurs in Monterrey, Mexico's financial hub.

Lopez Obrador remains a dogged, relentless campaigner. But time has worn on him. In 2006, middle-aged women described him as attractive and charismatic. Now he can often seem a bit tired or wobbly.

In a rare joke, Lopez Obrador quipped during a presidential debate that he might look older than he is because he'd been "broken in by dirt roads" after six years of unofficial campaigning. It isn't exactly an exaggeration.

After the final election results were announced last time, Lopez Obrador shut down the center of Mexico City, dubbed himself the "legitimate president" and embarked on a tour of the country to keep his base energized. He is now perhaps the only politician in modern history to have visited every one of the nation's 2,445 county seats — some several times over.

"There are only two paths," Lopez Obrador said in Tlaxcala, to roars of approval. "More of the same, or a true change. More of the same is more corruption, more injustice, more unemployment, more insecurity, more violence."

In his platform, Lopez Obrador is calling for an austerity plan of cuts in government salaries and an "attack on corruption" that would liberate funds for social programs. He proposes large-scale public works projects to boost employment, such as bullet trains to the U.S. border and a beefed-up transit corridor over Mexico's isthmus that could compete with the Panama Canal.

But many liberal voters do not share the same enthusiasm for the candidate that they might have in 2006.

A large segment of PRD supporters had hoped popular Mexico City Mayor Marcelo Ebrard would be the left's candidate this year, and perhaps draw undecided voters who have shunned another Lopez Obrador candidacy. (Lopez Obrador has said he would make Ebrard his interior minister.)

If he doesn't win on Sunday, Lopez Obrador told a business group, he will retire to his ranch in the state of Chiapas, which he comically named using a bit of Mexican slang that is unprintable.